Aphid transmission of a potyvirus depends on suitability of the helper component and the N terminus of the coat protein (original) (raw)
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Virology, 1997
Specific binding between the coat protein (CP) and the helper component (HC) of the tobacco vein mottling potyvirus (TVMV) was characterized using a protein blotting-overlay protocol. In this in vitro assay, HC interacted with either virions or CP monomers originating from the aphid-transmissible TVMV-AT but not from the non-aphid-transmissible TVMV-NAT. There was a strong correlation between the aphid transmissibility of a series of TVMV variants having mutations in the DAG motif of the CP and their ability to bind HC. Expression of TVMV CP derivatives in bacteria allowed a precise determination of the minimum domain mediating HC binding. This domain is composed of seven amino acids, including the DAG motif (DTVDAGK), located in the N-terminus of the TVMV CP at amino acid positions 2 to 8. ᭧ 1997 Academic Press 1 Permanent address: Station de Recherches de Pathologie Comany other motif) of the CP of potyviruses. paré e,
Role of the helper component in vector-specific transmission of potyviruses
Journal of General Virology, 1998
Four aphid species were tested for their ability to transmit tobacco etch (TEV) and turnip mosaic (TuMV) potyviruses. Myzus persicae and Aphis gossypii transmitted both viruses efficiently from infected plants, whereas Lipaphis erysimi transmitted only TuMV and Myzus ascalonicus was a poor or non-transmitter of either virus. Similar electrically monitored probing patterns were produced by M. persicae, L. erysimi and M. ascalonicus, ruling out behavioural differences as the cause of differential transmission. Transmission results similar to those from infected plants were obtained when these aphids acquired homologous virus/helper component (HC) mixtures through membranes. Methods Aphids. Two species, Myzus persicae and Aphis gossypii, were chosen for their general efficacy as potyvirus vectors. In experiments at Lexington (KY, USA), M. persicae was reared on mustard (Brassica perviridis) and A. gossypii on cucumber (Cucumis sativus). Lipaphis erysimi and Myzus ascalonicus were chosen for their potential as differential vectors and were reared on mustard and pansy (Viola wittrockiana),
Physiological and Molecular Plant Pathology, 2003
The amino terminus (NT) of the potyvirus coat protein (CP), which is necessary for aphid transmission and systemic infection, is externally located on the virion, strongly antigenic, and highly variable in length and sequence. Chimeras of Zucchini yellow mosaic virus (ZYMV) were constructed by substitution of the native CP-NT with CP-NTs of potyviruses with overlapping (Watermelon mosaic virus, WMV) and non-overlapping (Tobacco etch virus, TEV) host range. The chimeric viruses produced strong initial symptoms on ZYMVsusceptible cucurbits. Approximately 6 weeks post-inoculation, zucchini and cucumber plants infected with the TEV chimera, exhibited a distinct recovery characterized by a loss of symptoms on young leaves, reduced virus titer, and virus-specific protection against secondary infection. The chimeric viruses did not overcome naturally occurring ZYMV resistance in cucumber, ZYMV-CP-mediated resistance in transgenic melons, or expand host range to TEV-or WMV-susceptible species. These results demonstrate that despite substantial variability in length and sequence, the CP-NTs from heterologous potyviruses facilitated systemic infection in ZYMV-susceptible cucurbits, but were not sufficient to cause infection in non-ZYMV hosts. The observed recovery response with the non-cucurbit CP-NT suggests that the CP-NT is important for biological efficiency of the virus and/or adaptation of the virus to its host. q
Journal of General Virology, 1996
The hypothesis that loss of aphid transmissibility of potyvirus mutants is due to non-retention of virions in the mouthparts was tested by feeding aphids through membranes on purified virions of aphid transmissible (AT or HAT) and non-aphid-transmissible (NAT) tobacco vein mottling virus (TVMV) or tobacco etch virus (TEV), in the presence of functional [potato virus Y (PVY) HC or TVMV HC] or non-functional (PVC HC) helper component (HC). TVMV virions were detected, by electron microscopic examination of immunogoldlabelled thin sections, in the food canal or cibarium of 57 % of 28 aphids fed on the transmissible combination of TVMV-AT and functional HC, while no virions were found in these structures in 25 aphids fed on the nontransmissible combinations: TVMV-NAT and PVY HC, or TVMV-AT and PVC HC. Autoradiography of intact stylets allowed the examination of much larger numbers of aphids, fed on 125I-labelled TEV; 48 % of 523 aphids fed on the TEV-HAT and PVY HC combination retained label in the stylets; this correlated well with the percentage transmission in bioassays. In contrast, in non-transmissible combinations, label was found in the stylets of 0.77% of 389 aphids fed on TEV-NAT and PVY HC, and 1-35 % of 223 aphids fed on TEV-HAT and PVC HC. No differences were found in the overall amount of label in the bodies of aphids fed on the transmissible and non-transmissible combinations.
Journal of General Virology, 1995
The nature of the amino acids in the N-terminal 'DAGX' motif of the coat protein of tobacco vein mottling virus (TVMV) that have a direct effect on aphid transmissibility of the virion were further defined by sitedirected mutagenesis. In the first position of the DAGX motif, Asp or Asn are required for aphid transmissibility. In the second position, the nonpolar residue Ala, but not the nonpolar Gly or Val or the polar Thr and Ser, is compatible with transmissibility. In the third position, the small, neutral, nonpolar Gly appears to be critical; even substitution of Ala, with a minimal side-chain, drastically reduces transmissibility. Although the amino acid following the DAG sequence is not highly conserved among potyviruses, the presence of an acidic Glu or Asp residue at this position in the TVMV coat protein drastically reduces or abolishes aphid transmissibility. An attempt was made to test the hypothesis that trypsin cleavage of the N terminus is involved in the aphid inoculation process by destroying a trypsin cleavage site downstream from the DAGX motif. While the predicted decrease in transmission occurred from infected plants, there was no effect on the transmission of purified virus.
Archives of Virology, 1998
Aphid transmission of potyviruses depends on the presence of specific sequence domains in two virus encoded proteins, the coat protein (CP) and helper component-proteinase (HC-Pro). Aphid transmissable peanut stripe virus (PStV), like most potyviruses, has an Asp-Ala-Gly (DAG) motif in the amino-terminal part of the CP. Peanut Mottle Virus (PeMoV) was determined to be highly aphid transmissible but has a unique Asp-Ala-Ala-Ala (DAAA) motif. To determine if the DAAA motif could functionally replace the DAG motif in PStV, mutations were made in a full-length cDNA clone of PStV. All of the mutations in the CP DAG motif abolished aphid transmissibility of PStV but did not affect virus infectivity. The aphid transmissibility of the PStV-DAAA mutant was partially restored by feeding aphids an artificial diet containing purified virus and PeMoV HC-Pro. The PStV-DAAA virus was poorly transmitted by aphids in vitro with HC-Pro purified from PStV or tobacco vein mottling virus (TVMV) infected plants. These experiments support the theory that specific HC-Pro/CP interactions are required for efficient aphid transmission. Based upon the sequence comparisons of 16 potyviral HC-Pro proteins several conserved motifs and striking differences have been identified. PeMoV was determined to have an Ala-Ser-Cys (ASC) HC-Pro motif instead of a highly conserved Cys-Cys-Cys (CCC) motif. We have predicted that this CCC motif could play an important role in the specific interaction between the HC-Pro and the CP DAG motif.
European Journal of Plant Pathology, 1995
The behavioural events associated with acquisition of tobacco etch potyvirus by starved Myzus persicae during single, electrically-recorded penetrations of plants or a Parafilm membrane were compared. Twenty nine percent of aphids acquired virus from plants and subsequently transmitted to test plants. Stylet puncture of the plasmalemma, indicated by a potential drop (pd) to the intracellular signal voltage level, occurred during 84% of penetrations, and virus transmission was always associated with this behavioural event during acquisition. Periods of intracellular stylet tip location, known as pd phase II, ranged from 3.6-12.2s, and always comprised three consecutive sub-phases, designated II1, II2 and II3. Ninety six percent of pds included distinct pulses during phase I13. A waveform which closely resembled these pulses was produced by 59% of aphids that probed a virus suspension through a Parafilm membrane; nineteen percent of the aphids subsequently transmitted membrane-acquired virus and transmission was significantly associated with the occurrence of the phase II3-1ike pulses during acquisition. The duration of occurrence of recorded phase I13 pulses, either on plants or the in vitro system, did not influence the virus transmission efficiency of aphids. The association of virus uptake from aqueous suspension with a particular behavioural activity is discussed as evidence for the 'ingestion-egesfion' hypothesis for nonpersistent transmission. Starved aphids acquiring virus from infected leaf tissue or the in vitro system had significantly higher transmission efficiencies than non-starved aphids. Starved and non-starved insects were electrically-recorded penetrating the artificial membrane, and again there was a clear difference in transmission efficiency (starved aphids, 26%; non-starved aphids, 2%). The higher transmission efficiency of starved insects could not be explained by behavioural differences, and the results lend support to the hypothesis that non-behavioural factors determine the enhancement of potyvirus transmission by preacquisition starvation. Abbreviations: BMV = Beet mosaic virus; EMF = Electromotive force; HAT = Highly aphid-transmissible; HC = Helper component; pd --Potential drop; PVY --Potato virus Y; TEV = Tobacco etch virus.
Transgenic Research, 1999
Spread of the aphid nontransmissible Zucchini yellow mosaicvirus virus (ZYMV) strain MV was monitored over two consecutive years in field plots of nontransgenic and transgenic squash expressing the coat protein (CP) gene of the aphid transmissible strain FL of Watermelon mosaic virus (WMV). The experimental approach was to mechanically inoculate plants with ZYMV strain MV and to assess subsequent transmissions, assumed to be vectored by aphids, of this strain to nonmechanically inoculated plants. Strain MV was distinguished from other ZYMV isolates by a threonine at position 10 of the CP or by a distinct electrophoretic pattern of a Nla IV-digested genomic cDNA fragment generated by RT-PCR. ZYMV strain MV was not detected in fields of nontransgenic plants, but was apparently aphid transmitted to 77 of 3,700 plants (2%) in transgenic fields. Despite the availability of numerous test plants and conditions of high disease pressure but low selection pressure, an epidemic of ZYMV strain MV did not develop in fields of transgenic plants. In contrast, the aphid transmissible ZYMV strain NY was aphid-transmitted to 99% (446/450) of transgenic plants under similar conditions. The relevance of these results in assessing environmental risks of transgenic plants expressing CP transgenes is discussed.